(full paper is archived in the Miller Library)
Title: Over 20 year stablity in abalone population in an area
inhabited by sea otters
Student Author(s): Stoll, Nicolai
Faculty Advisor(s): Pearse, John
Location: UC Santa Cruz Kelp Forest Ecology Class
Date: Fall 1992
Keywords: HMLR, Haliotis rufescens
Abstract: One of the principle food items of the sea otter Enhydra lutris at Hopkins Marine Life Refuge, Pacific Grove CA, and throughout most of their present range is the abalone, Haliotis spp.(Costa 1978). The sea otter and the abalone coexisted for thousands of years in equilibrium (the nature of which is uncertain) on the Pacific coast until the 1800's when otters were hunted extensively for their fur. By the turn of the century the otter population had been reduced to near extinction levels. Laws protecting sea otters helped to revive the population from about 50 animals in 1911 to about 2000 animals off the central California coast in 1978, with otters returning to Hopkins Marine Life Refuge sometime in the 1960's. The otter's range in California has extended to a section of the coastline of about 250 km from Santa Cruz county to San Luis Obispo county (Hines and Pearse 1982).
Observations of McLean (1962) in the 1950's show that the sea floor at Hopkins Marine Life Refuge was densely populated with abaloanes "spaced only a few feet apart". This situation presents a very good opportunity to study the impact that the return of the otter has had on an abalone population in an area where otters had been absent for many decades. Since 1973 there has been a series of studies (Lowry and Pearse 1973, Cooper et al. 1977, Hines and Pearse 1982) which have examined a particular site at Hopkins Marine Life Refuge in respect to density, size frequency, mortality and turnover of the abalone population there. These studies have shown that although otters have continued to feed actively on abalones, and abalone size and density initially decreased dramatically, the population has remained stable since this decline, with high mortality balanced with high recruitment and growth rates. Abalone living within the otters range are strictly limited to the protection of cracks and crevices in rocks and are therefore highly dependent on substrate topography for maintenance of their population density.
Since 1981 (Hines and Peaarse 1982) there have been no follow up studies of abalone done at this specific site at Hopkins Marine Life Station (except Pollard 1992 which studied a nearby site and used diferent sampling techiques). This study was undertaken to see (1) if the stability of the abalone population has persisted, (2) if there has been any change in the size frequency distribution, and (3) if high turnover rates persist.